The present invention relates to thermoplastic compositions based on syndiotactic polymers of styrene, reinforced with inorganic and/or organic rigid fillers.
More specifically this composition comprises:
a) 100-80% by weight of a crystalline syndiotactic polymer of styrene;
b) 0-20% by weight of a polyarylene-ether;
c) 1-200 parts by weight, with respect to 100 parts of (a)+(b), of one or more inorganic and/or organic rigid fillers;
d) 0.01-5 parts by weight, with respect to 100 parts of (a)+(b), of a silanic compound having general formula (I): 
wherein
R and R1 are, independently, hydrogen or an alkyl radical containing from 1 to 8 carbon atoms;
R2 is a hydrolyzable alkoxyl group containing from 1 to 6 carbon atoms or a halogen atom;
R3 is an alkyl radical containing from 1 to 8 carbon atoms;
X is either a radical having the formula 
xe2x80x83or an aromatic or cycloaliphatic or heterocyclic radical, wherein R4 is hydrogen or an alkyl radical containing from 1 to 18 carbon atoms and n is an integer between 1 and 4;
m is an integer between 1 and 3.
The compositions claimed have improved thermal properties, creep resistance and impact strength with a consequent increase in rigidity and shock-resistance properties and they can be used for applications in the field of household appliances and in the electronic and car industries.
It is known that styrene polymers have a good rigidity but poor resistance to solvents, heat and impact; the discovery of new catalysts has recently allowed the synthesis of polystyrenes with a high degree of syndiotaxy, which are crystalline rather than amorphous, very rigid and with a high melting point.
Owing to the different molecular conformation, these new polystyrenes have reasonable resistance to heat and solvents but retain the fragility of the atactic polymer.
In an attempt to improve both resistance to creep deformation (induced by a constant loading, generally at high temperatures) and impact, efforts have been made to reinforce the new polymer with inorganic fibres.
As, to obtain this result, it is necessary to have good adhesion between the fibre and polymeric matrix, research has been directed towards determining under what conditions this can be achieved.
In this respect, the U.S. document U.S. Pat. No. 5,426,171 (Huang et al.) describes the use of small amounts of polyphenylene-ethers grafted with maleic anhydride (PPO-g-MAH) associated with a silane, both operating on the polymer and sizing the glass fibre.
U.S. Pat. No. 5,270,353 (Nakano et al.), on the other hand, claims a composition comprising a styrene polymer having a syndiotactic configuration, a styrene polymer modified with epoxy groups and a sized inorganic filler, to favour compatibilization between the components.
In U.S. Pat. No. 5,395,890 (Nakano et al.), a rubber and/or inorganic filler is added to the styrene polymer/thermoplastic resin (generally PET) mixture to improve the heat resistance and impact strength.
The patent EP 0 314 146 (Albizzati et al.), on the other hand, relates to a composition based on syndiotactic styrene polymers and polyphenylene-ethers (PPO) which, also in this case, has improved mechanical properties compared with compositions containing amorphous or isotactic polystyrene.
U.S. Pat. No. 5,412,024 (Okada et al.) describes thermo plastic compositions which comprise syndiotactic polymers whose modified end-group is bound to compounds having polar groups in the presence of an inorganic filler.
U.S. Pat. No. 5,436,397 (Okada et al.) describes a composition with improved mechanical properties comprising a polystyrene resin as such and modified, an elastomeric compound and an inorganic filler.
In conclusion, all the compositions claimed, either limit themselves to facing the problem of impact strength by using rubbers (which however reduce the rigidity and heat resistance) or try to solve the problem of adhesion matrix/filler by both modifying the polymer by the introduction of particular reactive groups, and covering the filler with substances which favour adhesion; in all cases however, the process is complicated and incomplete.
On the other hand, there are also documents that describe the use of compatibilizing compounds applied to polypropylene reinforced with mica (EP 0 69 937xe2x80x94Moro et al.) or, more generally, to reinforced polyolefins (EP 0 370 551xe2x80x94Joslyn et al.).
The Applicant has now overcome the above drawbacks by preparing a mixture in a single phase, which comprises syndiotactic styrene polymer to which small amounts of a polyarylate, a rigid filler and a particular compatibilizing compound are generally added, without the necessity, therefore, of preparing the polymeric matrix for adhesion with the filler by means of particular pretreatment processes.
The present invention consequently relates to thermoplastic compositions based on syndiotactic polymers of styrene, reinforced with inorganic and/or organic rigid fillers.
More specifically this composition comprises:
a) 100-80% by weight of a crystalline syndiotactic polymer of styrene;
b) 0-20% by weight of a polyarylene-ether;
c) 1-200 parts by weight, with respect to 100 parts of (a)+(b), of one or more inorganic and/or organic rigid fillers;
d) 0.01-5 parts by weight, with respect to 100 parts of (a)+(b), of a silanic compound having general formula (I): 
xe2x80x83wherein
R and R1 are, independently, hydrogen or an alkyl radical containing from 1 to 8 carbon atoms;
R2 is a hydrolyzable alkoxyl group containing from 1 to 6 carbon atoms or a halogen atom;
R3 is an alkyl radical containing from 1 to 8 carbon atoms;
X is either a radical having the formula 
xe2x80x83or an aromatic or cycloaliphatic or heterocyclic radical, wherein R4 is hydrogen or an alkyl radical containing from 1 to 18 carbon atoms and n is an integer between 1 and 4;
m is an integer between 1 and 3.
A preferred form of this composition is the following:
a) 100-95% by weight of a crystalline syndiotactic polymer of styrene;
b) 0-5% by weight of a polyarylene-ether;
c) 10-70 parts by weight, with respect to 100 parts of (a)+(b), of one or more inorganic and/or organic rigid fillers;
d) 0.1-3 parts by weight, with respect to 100 parts of (a)+(b), of a compound having general formula (I), described above.
Component (a) is given by a styrene homo- or co-polymer with a prevalently syndiotactic configuration; this means that the stereostructure of the polymer has phenyl or phenyl-substituted side groups situated alternately in opposite directions with respect to the main chain represented according to a Fisher projection.
The preparation of these polymers can be carried out, according to what is known in the art, in bulk, solution or suspension, at temperatures generally ranging from xe2x88x9250 to 120xc2x0 C. and pressures generally ranging between 0.1 and 5 atmospheres, using catalytic systems containing as main components a titanium complex (for example TiX4, CpTiX3, Cp*TiX3, with Cp=cyclopentadienyl, Cp*=pentamethylcyclopentadienyl, X=alkyl, alkoxide, halogen, carboxylate, dialkylamine, etc., and the various X can also be different from each other) and a co-catalyst selected from an alkylaluminoxane (preferably methylaluminoxane) or a derivative of tris(pentafluorophenyl)boron.
The catalytic system may optionally also contain other activator components such as aluminum alkyls or tin alkyls, etc. (see, for example, EP 0 780 405).
The degree of taxis can be quantitatively determined by means of NMR (Nuclear Magnetic Resonance) of carbon 13 according to the method described in U.S. Pat. No. 4,680,353.
The styrene polymers with a prevalently syndio-tactic configuration mentioned in this composition comprise, among others, homo- and co-polymers containing styrene, ortho-, meta- and para-substituted alkylstyrenes, ortho-, meta- and para-substituted halogen alkylstyrenes (or mixtures of these two polymers), with a degree of syndiotaxy, measured according to the method indicated, which is such that the proportion of racemic dyads is at least 75% or preferably higher than 85%, or, even better, 95%, and the proportion of racemic pentads is at least 30%, or, preferably, 50%; however the polymer which is particularly suitable is polystyrene.
The polyarylene-ether (b) is a polymer or copolymer comprising a sequence of basic units which can be represented by the following general formula: 
wherein n is an integer between 50 and 1000, R5 and R6, the same or different, are hydrogen, halogens such as F, Cl or Br, hydrocarbon radicals which do not contain tertiary carbons in a position (for example, methyls, ethyls, n-propyls, n-butyls), halogenated or hydroxyha-logenated hydrocarbon radicals containing at least 2 carbon atoms between the benzene ring and the halogen and without tertiary carbons in position xcex1 [for example xe2x80x94(CH2)2Cl, xe2x80x94(CH2)2Br, xe2x80x94(CH2)3Cl, xe2x80x94(CH2)3Br].
The most preferable is poly(2,6-dimethyl-1,4-phenylene-ether), generally known as PPO, with an intrinsic viscosity [xcex7] measured in chloroform at 23xc2x0 C., ranging from 0.28 to 0.70 dl/g, preferably 0.50 dl/g.
The rigid fillers (c) comprise inorganic and/or organic fillers with an aspect ratio or, in the case of fibres, length with respect to diameter (L/D) higher than 5 and include, among others, glass fibres, ceramic whiskers, wollastonite, mica, carbon fibres and aramidic fibres; glass fibre is preferable with a length of 0.1 to 10 mm and L/D ranging from 5 to 100.
These fillers, optionally calcined, may also comprise a surface coating, generally based on silanic compounds or titanates, which induce better adhesion between the filler and polymeric matrix.
When glass fibre is used in particular, this can also be sized with solutions of appropriate compatibilizing agents before mixing with the other components or, if already sized (for example in the case of a commercial filler), it may undergo an additional sizing with suitable solutions.
The various compatibilizing agents comprise silanic compounds and titanates and, for example, xcex3-amino-propyl-triethoxysilane is particularly suitable.
Compound (d) is described by formula (I); among the silanes described in this formula, those in which R and R1 are hydrogen atoms, R2 is an alkoxyl radical containing from 1 to 4 carbon atoms (for example, xe2x80x94Oxe2x80x94CH3, xe2x80x94Oxe2x80x94C2H5, xe2x80x94Oxe2x80x94C3H7 or xe2x80x94Oxe2x80x94C4H9), R4 is a hydrogen, n is 2 or 3 and m is equal to 0, are preferable.
Maleamic silane defined as SiMA is particularly indicated, which can be distinguished by the following formula: 
and is prepared according to the process described in EP 0 69 937, whose content is an integrating part of the present application.
The composition of the present invention may optionally contain antioxidants, nucleating agents, stabilizers and process aids.
Antioxidants which can be used are those containing phosphorous such as monophosphites, diphosphites and phosphonites, for example tris(2,4-di-ter-butylphenyl)phosphite, di-nonyl-phenyl phosphite, di-stearyl-pentaerythritol-di-phosphite, tetrakis(2,4-di-ter-butyl-phenyl)4,4xe2x80x2-biphenylene-di-phosphonite and diphosphites generally represented by the formula: 
wherein R7 and R8 both represent alkyl groups comprising from 1 to 20 carbon atoms, cycloalkyl groups with 3-20 carbon atoms or aryl groups with 6-20 carbon atoms; bis(2,4-di-ter-butyl-phenyl)-pentaerythritol-di-phosphite, commercially known as Ultranox 626 of General Electric, is particularly suitable.
Another group of antioxidants suitable for the purpose, are those based on sterically hindered phenols and therefore, among others, 2,6-di-ter-butyl-4-methyl-phenol, 2,6-di-phenyl-4-methoxy-phenol, bis[3-(5-ter-butyl-4-hydroxy-m-tolyl)propionate] of ethylenebis-oxy-ethylene, 1,1,3-tris(2-methyl-4-hydroxy-5-ter-butyl-phenyl)butane and, preferably, tetrakis[3-(3,5-di-ter-butyl-4-hydroxy-phenyl)propionate] of pentaerythritol, commercially known as Irganox 1010 of Ciba-Geigy.
A final group of antioxidants is represented by sulfur compounds, such as thioethers, among which di-lauryl-3,3xe2x80x2-thio-di-propionate, di-stearyl-3,3xe2x80x2-thio-di-propionate and, preferably, pentaerythritol-tetra-kis-(xcex2-lauryl-thiopropionate).
These antioxidants can be added in a mixture in weight percentages ranging from 0.01 to 1 with respect to the polymer, with ratios [phosphorous compounds]/[phenol compounds]/[sulfur compounds] ranging from 50/10/1 to 0.5/1/1 and preferably from 10/10/1 to 1/1/1.
The couple Irganox 1010/Ultranox 626 in a weight ratio of 1/5 for a total of 0.5-1 parts per 100 parts of polymer, is particularly effective.
Among nucleating agents for the crystallinity, metal salts of organic acids, among which sodium or aluminum benzoate, or, preferably extra-fine talc, can be mentioned; these nucleating agents can be added to the composition in a quantity of 0.1-5 parts by weight per 100 parts of polymer and, preferably, 0.5-2.
Finally, it is also possible to add quantities of rubber to the composition to provide better impact strength, for example, ethylene-propylene rubbers (EPR), ethylene-propylene-diene rubbers (EPDM), or, preferably, copolymers containing a styrene polymer, among which styrene-butadiene-styrene (SBS), hydrogenated styrene-butadiene-styrene (SEBS), acrylonitrile-butadiene-styrene (ABS) rubbers; these rubbers can be added to the compound in percentages ranging from 0 to 100 by weight.
The process for the preparation of the composition in question comprises a first method which consists in dry-mixing the four components (a), (b), (c) and (d), and subsequently treating this compound in a mixing apparatus at temperatures ranging from 270 to 320xc2x0 C., preferably 280xc2x0 C., with a number of revs ranging from 50 to 200 rpm, preferably 100 rpm, and for a time ranging from 4 to 10xe2x80x2.
Equipment for the mixing of polymers in the molten state such as single-screw and twin-screw extruders, plastographs and Banbury mixers can be used for the purpose.
The second method consists in a pretreatment, at temperatures ranging from 270 to 320xc2x0 C., of the resin based on polystyrene (a) in the mixing apparatus defined above until the complete melting of the polymer, followed by the addition of components (b), (c) and (d).
The composition of the present invention has a high modulus, resistance to hydrolysis and heat with consequent improved thermal properties making it useful for applications at high temperatures.